Suggested by Destroyer Destoroyah is a powerful Kaiju capable of causing great calamity to any who opposes him. That said, he doesn’t have the speed to keep up with someone like Roy. Roy is a master swordsman who strikes with the Burning Blade. He has nothing to fear from Destoroyah as no attack will be able to tag him. Roy will quickly wither Destoroyah’s defenses down until one last strike ends things for good. Roy wins.
I think you underestimate Destoroyah. Since his means of summoning is using a Oxygen Destroyer, Roy still needs that to breathe, and Destoroyah’s summoning means that something beyond the ability of the Godzilla-verse Japanese Government has happened.
It’s true that he needed that to be created but in the match he already exists so that wouldn’t have the same effect. That being said, Roy still has the complete advantage in speed and power so he should be able to overwhelm Destoroyah in those two areas right away